Which structure of protein remains intact after coagulation of egg white on boiling?

The optically inactive amino acid is

$A$ zwitter ion is

Which of the following is capable of forming a zwitter ion?

Identify the acidic amino acid from the following (represented by using three-letter symbols).

$1.78 \ g$ of an optically active $L$-amino acid $(A)$ is treated with $NaNO_{2} / HCl$ at $0^{\circ}C$. $448 \ cm^{3}$ of nitrogen at $STP$ is evolved. $A$ sample of protein has $0.25 \%$ of this amino acid by mass. The molar mass of the protein is